Identify duplicate rows using `GROUP BY` and `HAVING COUNT(*) > 1`
Use `ROW_NUMBER()` to rank duplicates within each group
Delete rows where `ROW_NUMBER() > 1`
Keep one row per duplicate group using a CTE or subquery
Use a unique key or primary key to target rows for deletion
Create a backup before deleting duplicate data
Add a `UNIQUE` constraint to prevent future duplicates
Use `SELECT DISTINCT` when you only need unique results in a query
Use `INSERT INTO new_table SELECT DISTINCT …` to rebuild a deduplicated table
Verify the remaining rows after deletion